I. Field of the Invention
The present invention relates generally to electronic alarm systems for controlling a plurality of strobe devices connected to an alarm control panel. More particularly, the present invention relates to an electronic alarm system having one or more loops of strobe devices whereby all of the strobe devices along a single loop operate to flash in sync.
Strobe devices that emit light are typically used in alarm systems, such as fire alarm systems, to visually alert people in a protected area of an emergency situation. Such alarm systems may also include other types of notification appliances, such as an audible signaling appliance or horn. Ideally, strobe devices are situated throughout an entire building to ensure proper protection of all areas. Thus, any person in the building would be in viewing range of at least one strobe device.
In order to ensure proper coverage, it is quite common to have more than one strobe device in a single viewing area. For prior art strobe designs, the timing for flashing the strobe light is controlled by each individual device. Since each strobe device runs independently, it would be common for two or more devices to flash out of sync or sequence with respect to each other. Even when devices initially flash in sync, the flash interval for the devices may slowly drift apart after a certain period of time, resulting in a flash followed by another flash shortly thereafter.
A problem that occurs with having two or more non-synchronized strobe devices within a single viewing range is that a photoconvulsive response may be triggered in individuals having photosensitive conditions. In particular, a person suffering from epilepsy may have a seizure by viewing a high frequency of light flashes. Although the flash rate of a single device can be controlled, the composite flash rate of a plurality of non-synchronized devices could produce a high frequency of light flashes and potentially trigger a convulsive reaction. Underwriters Laboratory has stated that epileptic seizures are not necessarily instituted by multiple flashes alone, but are more directly caused by any two flashes within 0.2 seconds. Likewise, the United States Department of Transportation, in view of the Americans with Disabilities Act Accessibility Guidelines, has taken a similar position and further stated that two or more non-synchronized devices within a single viewing area than can produce a composite flash rate that could trigger an epileptic seizure.
II. Description of the Prior Art
Strobe devices that produce a light flash at a set frequency are known. For example, U.S. Pat. No. 4,952,906 to W. P. Buyak, et al. titled STROBE ALARM CIRCUIT provides a strobe light circuit for flashing a strobe flash unit at a desired frequency, even when changes in its supply voltage occur. For this strobe light circuit, a switch controls the charging of a inductor by a power source and the discharging of the inductor to a capacitor and flash unit combination. The switch is opened when the inductor current reaches a predetermined value, and the switch is closed in response to a timing signal having a regular period. The frequency does not vary since the same amount of energy is stored in the inductor for each cycle of the switch.
It is also known that microcontrollers may be used to control the flash rate of a light signal device. For example, U.S. Pat. No. 4,935,951 to G. J. Robinson, et al., which issued on Jun. 19, 1990, provides an emergency telephone actuated signal light having a microcontroller for comparing the dialed numbers with a stored emergency number. Also, U.S. Pat. No. 5,341,069 to J. Kosich, et al., which issued on Aug. 23, 1994, provides a strobe light circuit having a microcontroller for triggering a flashtube at a predetermined rate.
However, none of the above U.S. patents provide any way of synchronizing a plurality of strobe devices in order to avert a composite flash rate that could trigger a convulsive reaction, such as an epileptic seizure. Thus, there is a need for a system for synchronizing a plurality of strobe devices so that they flash in sync with each other, especially synchronizing two or more devices within the same viewing area. Such a system should avert a situation where an individual, particularly a person susceptible to photoconvulsive reactions, would view more than one light flash within a short period of time and have a convulsive reaction.
Against the foregoing background, it is a primary object of the present invention to provide a synchronous strobe system of an alarm system that synchronizes a plurality of strobe devices so that the strobe light of all strobe devices flash at the same time.
It is another object of the present invention to provide such a synchronous strobe system in which a synchronization signal is transmitted throughout the strobe loop to provide the strobe devices with a reference signal to synchronize all of their flashes.
It is a further object of the present invention to provide such a synchronous strobe system in which each of the strobe devices has electronic circuitry, including a microcontroller, to detect the synchronization signal and flash the strobe light based on the signal.
It is still further object of the present invention to provide such a synchronous strobe system in which each of the strobe devices may operate in a Sync required mode or Sync not required mode. For Sync required mode, the synchronization signal must be detected by the strobe device to flash a strobe light of the strobe device. Otherwise, the microcontroller waits for the next synchronization signal before attempting to flash the strobe light. For Sync not required mode, the strobe light is flashed at an independent flash rate until the synchronization signal is detected and used to realign the flash rate.